Solid lithium ion conducting electrolytes and methods of preparation

ABSTRACT

A composition comprised of nanoparticles of lithium ion conducting solid oxide material, wherein the solid oxide material is comprised of lithium ions, and at least one type of metal ion selected from pentavalent metal ions and trivalent lanthanide metal ions. Solution methods useful for synthesizing these solid oxide materials, as well as precursor solutions and components thereof, are also described. The solid oxide materials are incorporated as electrolytes into lithium ion batteries.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 12/824,350filed on Jun. 28, 2010, the contents of which are incorporated herein byreference in their entirety.

This invention was made with government support under Contract NumberDE-AC05-00OR22725 between the United States Department of Energy andUT-Battelle, LLC. The U.S. government has certain rights in thisinvention.

FIELD OF THE INVENTION

The present invention relates to the field of lithium ion conductingelectrolytes, and particularly, to such electrolytes that are solid, andmore particularly, solid oxide electrolytes.

BACKGROUND OF THE INVENTION

As liquid organic and polymer electrolytes continue to pose a majorsafety concern and shortened lifetime for current lithium ion batteries,solid lithium ion conducting electrolytes are sought for replacingliquid organic and polymer electrolytes. However, there are manydifficulties being encountered in efforts to make solid electrolytesthat possess the set of optimal characteristics needed to at leastmaintain such properties as the power output, charge/dischargeefficiencies, capacity rating, and lifetime of current liquid andpolymer electrolyte lithium batteries. In particular, it is highlydesired for the solid electrolyte to exhibit high lithium ionconductivity, along with a negligible electronic conductivity, highelectrochemical stability, and long-term stability against reactionswith electrode materials.

Although some materials with such properties have been produced, theirintegration into lithium ion batteries as electrolytes has beensignificantly limited by the solid-state methods of synthesis currentlyused in preparing these materials. The solid state methods of synthesispossess numerous drawbacks, including the inability to adjust oroptimize the particle size of the solid materials, or to render thesolid material as a film, and particularly, thin films (e.g., up to orless than 1 micron) of uniform thickness. Another significant drawbackof current solid-state methods of synthesis is their prohibitive costand resistance to production scale up. A further significant drawback ofcurrent solid-state methods is their inability to be integrated intoexisting lithium ion battery assembly line manufacturing processes.

SUMMARY OF THE INVENTION

In a first aspect, the invention is directed to a heterometallicalkoxide composition useful for the solution synthesis of a lithium ionconducting solid oxide material, herein also referred to as an “oxidematerial” or “solid oxide”. In a particular embodiment, theheterometallic alkoxide includes at least one pentavalent metal, atleast one metal selected from trivalent lanthanide metals and alkalineearth metals, and negatively charged ligands, at least one of which isan alkoxide ligand.

In a second aspect, the invention is directed to a precursor solutionfor producing a lithium ion conducting solid oxide material. Theprecursor solution contains components that, upon contact with water oracetone, will produce an initial material (i.e., via hydrolysis) thatcan be converted to the final solid oxide material. In particularembodiments, the precursor solution includes a non-aqueous solventhaving dissolved therein lithium ions, and at least one type of metalion selected from pentavalent metal ions and trivalent lanthanide metalions, and negatively charged ligands, at least a portion of which arealkoxide ligands. In further embodiments, the precursor solutionincludes a non-aqueous solvent having dissolved therein lithium ions, atleast one type of pentavalent metal ion, at least one type of metal ionselected from trivalent lanthanide metal ions and alkaline earth metalions, and negatively charged ligands, at least a portion of which arealkoxide ligands. In the precursor solution, it is particularlyadvantageous in some embodiments that an excess molar amount of lithiumis present in the precursor solution relative to the stoichiometricratio of lithium in the solid oxide material to be produced.

In a third aspect, the invention is directed to a composition thatcontains lithium-containing solid oxide nanoparticles. Preferably, thenanoparticles have a composition that makes them useful as a lithium ionconducting solid electrolyte material. In particular embodiments, thenanoparticles include an oxide material containing therein lithium ions,and at least one type of metal ion selected from pentavalent metal ionsand trivalent lanthanide metal ions. In further embodiments, thenanoparticles include an oxide material containing therein lithium ions,pentavalent metal ions, and at least one type of metal ion selected fromtrivalent lanthanide metal ions and alkaline earth metal ions.

In a fourth aspect, the invention is directed to a lithium ion batterycontaining any of the above-described solid oxide compositions as anelectrolyte. In particular embodiments, the solid oxide electrolytematerial is in the form of a film, e.g., sandwiched between an anode andcathode of the battery, and in particular embodiments, in direct contactwith the anode and cathode of the battery.

In a fifth aspect, the invention is directed to a method of preparing alithium ion conducting solid electrolyte material, such as the solidoxide materials described above. In particular embodiments, the methodis useful for preparing a lithium ion conducting solid oxide electrolytematerial containing lithium ions and at least one type of metal ionselected from pentavalent metal ions and trivalent lanthanide metalions. The method includes subjecting a precursor solution to hydrolysisconditions to produce an initial solid or gel, followed by pyrolysis ofsaid initial solid or gel, wherein the precursor solution includes anon-aqueous solvent having dissolved therein the metal species desiredto be included in the solid oxide material, i.e., lithium ions, and atleast one type of metal ion selected from pentavalent metal ions andtrivalent lanthanide metal ions, as well as negatively charged ligands,at least a portion of which are alkoxide ligands. In further embodimentsof the above-described method, the lithium ion conducting solid oxideelectrolyte material includes lithium ions, at least one type ofpentavalent metal ion, and at least one type of metal ion selected fromtrivalent lanthanide metal ions and alkaline earth metal ions, and theprecursor solution includes a non-aqueous solvent having dissolvedtherein the metal species desired to be included in the solid oxidematerial, i.e., lithium ions, at least one type of pentavalent metalion, at least one type of metal ion selected from trivalent lanthanidemetal ions and alkaline earth metal ions, as well as negatively chargedligands, at least a portion of which are alkoxide ligands. In particularembodiments of the above-described methods, an excess molar amount oflithium is present in the precursor solution relative to thestoichiometric ratio of lithium in the lithium ion conducting solidelectrolyte material to be produced.

The preparative methods described herein for synthesizing these solidoxide materials overcome numerous obstacles of conventional solid-statepreparative methods. Some advantages of the solution methods describedherein include their simplicity, lowered cost, their amenability inscaling up production and being integrated into existing lithium ionbattery assembly line manufacturing. Furthermore, the preparativemethods described herein are amenable for producing nanoparticles,films, and coatings of these oxide materials, and particularly, thinfilms and coatings (e.g., up to or less than 1 micron), as well asuniform films and coatings of these oxide materials.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. XRD pattern of Li₅La₃Nb₂O₁₂ pure solid oxide product preparedfrom a mixture of Li(OR), La(OR)₃, and Nb(OR)₅ in a 10:3:2 molar ratioin THF (excess of lithium used).

DETAILED DESCRIPTION OF THE INVENTION

In one aspect, the invention is directed to a solid oxide compositionuseful as a lithium-conducting electrolyte material. The chemicalcomposition of the solid oxide composition considered herein can be anyof the known chemical compositions of lithium-containing solid oxidematerials.

In a first set of embodiments, the solid oxide material consideredherein is, or includes, an oxide composition that includes lithium ionsand at least one type of pentavalent metal ion. The pentavalent metalion can be any element having a charge of +5, such as, for example,pentavalent niobium (Nb⁺⁵), tantalum (Ta⁺⁵), or antimony (Sb⁺⁵). In someembodiments, only one type of pentavalent metal ion is included (such asany one of the foregoing types), while in other embodiments, two, three,or more different pentavalent metal ions are included. Some examples ofsuch oxide materials include those of the generic formula LiMO₃, whereinM represents one or more pentavalent metal ions. When M represents morethan one pentavalent metal ion, the oxide materials can further berepresented by the formula LiM¹ _(x)M² _(y)M³ _(z)O₃, wherein each ofM¹, M², and M³ are different pentavalent metal ions, and x, y, and z sumto 1. In particular embodiments, x, y, and z are independentlyprecisely, at least, or no more than 0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5,0.6, 0.7, 0.8, 0.9, 0.095, or ranges therein, as long as x, y, and z sumto 1. Some particular examples of such oxide materials include LiNbO₃,LiTaO₃, LiSbO₃, LiPO₃, LiAsO₃, LiNb_(0.5)Ta_(0.5)O₃,LiNb_(0.4)Ta_(0.6)O₃, LiNb_(0.5)Sb_(0.5)O₃, LiNb_(0.4)Sb_(0.6)O₃,LiTa_(0.5)Sb_(0.5)O₃, LiTa_(0.4)Sb_(0.6)O₃, Li_(0.5)Na_(0.5)NbO₃,Li_(0.55)K_(0.5)NbO₃, and Li_(0.5)Na_(0.5)Nb_(0.5)Ta_(0.5)O₃.

In a second set of embodiments, the oxide material considered herein is,or includes, an oxide composition that includes lithium ions, and atleast one type of trivalent lanthanide metal ion. The lanthanide metalcan be any of the elements of the Periodic Table of the Elements havingan atomic number of 57 to 71. In different embodiments, the lanthanidemetal is selected from one, two, three, or more of the followingelements: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium(Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd),terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm),ytterbium (Yb), and lutetium (Lu). In particular embodiments, at leastone of the lanthanide metals is La. Some examples of such oxidematerials include those of the generic formula LiLnO₂ and Li₂LnO₂,wherein Ln represents any one or more of the lanthanide elementsdescribed above.

In a third set of embodiments, the solid oxide material consideredherein is, or includes, an oxide composition that includes lithium ions,at least one pentavalent metal ion, and, in addition, at least one typeof trivalent lanthanide metal ion. Some examples of such oxide materialsinclude those of the formula LiMO₃ and subformulas therein doped withone or more lanthanides (e.g., LiMO₃:Ln, wherein Ln represents one ormore lanthanide metals), as well as those of the formulas LiLnO₂ orLi₂LnO₂ doped with one or more pentavalent metal ions (e.g., LiLnO₂:M orLi₂LnO₂:M, wherein M represents one or more pentavalent metal ions).

In further embodiments, the oxide material includes lithium ions, atleast one type of pentavalent metal ion and/or at least one type oftrivalent lanthanide metal ion, and, in addition, at least one type ofalkaline earth metal ion. The alkaline earth metal ion can be any of theelements in Group IIA of the Periodic Table. In different embodiments,the alkaline earth metal is selected from one, two, three, or more ofthe following elements: beryllium (Be), magnesium (Mg), calcium (Ca),strontium (Sr), barium (Ba), and radium (Ra). In one particular set ofembodiments, at least one of the alkaline earth metals is Mg. In anotherparticular set of embodiments, at least one of the alkaline earth metalsis Ca. In another particular set of embodiments, at least one of thealkaline earth metals is Sr. In another particular set of embodiments,at least one of the alkaline earth metals is Ba. Some examples of oxidecompositions containing lithium ions, pentavalent metal ions, andalkaline earth metal ions include those of the formula LiMO₃ andsubformulas therein doped with one or more alkaline earth ions (e.g.,LiMO₃:AX, wherein A represents one or more alkaline earth metals and Xrepresents one or more anions to charge balance with A; in particularembodiments, X is an oxide, sulfide, selenide, or telluride anion). Someexamples of oxide compositions containing lithium ions, trivalentlanthanide metal ions, and alkaline earth metal ions include those ofthe formulas LiLnO₂ or Li₂LnO₂ doped with one or more alkaline earthmetal ions (e.g., LiLnO₂:AX or Li₂LnO₂:AX, wherein AX has been definedabove).

In yet other embodiments, the oxide material includes at least onealkali metal ion other than lithium ion, such as those alkali metalsselected from sodium (Na), potassium (K), rubidium (Rb), and cesium(Cs). In yet other embodiments, the oxide material includes at least onetransition metal ion (i.e., either in place of or in addition to Nband/or Ta). The transition metal ion can be a first row, second row, orthird row transition metal, and main group elements can be from groupIIIA-VA, provided that a garnett structure can be retained. Someexamples of such materials include Li₅Ln₃M₂O₁₂, where M is a Group VBelement (V, Nb, Ta); Li₆ALa₂MO₁₂, where A is Ca, Sr, and/or Ba, and M isa Group VB element (V, Nb, Ta); Li₃Ln₃Te₂O₁₂ (Ln is one or more of anyof the lanthanide elements, particularly Y, Pr, Nd, or one or moreelements having atomic numbers of 62-71, i.e., Sm to Lu); Li₃Ln₃W₂O₁₂(Ln is one or more of any of the lanthanide elements, particularly Y,Pr, Nd, or one or more elements selected from Sm to Lu);Li_(5.5)La₃Nb_(1.75)In_(0.25)O₁₂; and Li_(5.5)La_(2.75)K_(0.25)Nb₂O₁₂.

In particular embodiments, the oxide material is, or includes, amaterial having one or both of the following formulas:Li_(5+x)Ln₂AM₂O_(11.5+0.5x)  (1)andLi_(5+y)A_(y)Ln_(3−y)M₂O₁₂  (2)

In formulas (1) and (2) above, A represents at least one alkaline earthmetal, M represents at least one pentavalent metal, Ln represents atleast one trivalent lanthanide metal, and x and y are, independently,generally a number of 0 to 2. In particular embodiments, x and/or y isindependently a number of 0, 0.5, 1, 1.5, or 2, or within a rangebounded by any of these values.

Some sub-generic classes of formula (1) considered herein includeLi₅Ln₂AM₂O_(11.5), Li₅La₂AM₂O_(11.5), Li₅Ln₂CaM₂O_(11.5),Li₅Ln₂SrM₂O_(11.5), Li₅Ln₂BaM₂O_(11.5), Li₅Ln₂ANb₂O_(11.5),Li₅Ln₂ATa₂O_(11.5), Li₅Ln₂ASb₂O_(11.5), Li₅Ln₂MgM₂O_(11.5) (where M isNb, Ta, or Sb, and Ln is any lanthanide, or more particularly, La and/orCe), Li₅Ln₂CaM₂O_(11.5) (where M is Nb, Ta, or Sb, and Ln is anylanthanide, or more particularly, La and/or Ce), Li₅Ln₂SrM₂O_(11.5)(where M is Nb, Ta, or Sb, and Ln is any lanthanide, or moreparticularly, La and/or Ce), Li₅Ln₂BaM₂O_(11.5) (where M is Nb, Ta, orSb, and Ln is any lanthanide, or more particularly, La and/or Ce),Li₆Ln₂AM₂O₁₂, Li₆La₂AM₂O₁₂, Li₆Ln₂CaM₂O₁₂, Li₆Ln₂SrM₂O₁₂, Li₆Ln₂BaM₂O₁₂,Li₆Ln₂ANb₂O₁₂, Li₆Ln₂ATa₂O₁₂, Li₆Ln₂ASb₂O₁₂, Li₆Ln₂CaM₂O₁₂ (where M isNb, Ta, or Sb, and Ln is any lanthanide, or more particularly, La and/orCe), Li₆Ln₂SrM₂O₁₂ (where M is Nb, Ta, or Sb, and Ln is any lanthanide,or more particularly, La and/or Ce), and Li₆Ln₂BaM₂O₁₂ (where M is Nb,Ta, or Sb, and Ln is any lanthanide, or more particularly, La and/orCe).

Some examples of compositions according to formula (2) includeLi₅Ln₂M₂O₁₂, Li₅La₂M₂O₁₂, Li₅Ln₂Nb₂O₁₂, Li₅Ln₂Ta₂O₁₂, Li₅Ln₂Sb₂O₁₂,Li₅Ln₂M₂O₁₂ (where M is Nb, Ta, or Sb, and Ln is any lanthanide, or moreparticularly, La and/or Ce), Li₆Ln₂AM₂O₁₂, Li₆La₂AM₂O₁₂, Li₆Ln₂ANb₂O₁₂,Li₆Ln₂ATa₂O₁₂, Li₆Ln₂ASb₂O₁₂, Li₆Ln₂MgM₂O₁₂ (where M is Nb, Ta, or Sb,and Ln is any lanthanide, or more particularly, La and/or Ce),Li₆Ln₂CaM₂O₁₂ (where M is Nb, Ta, or Sb, and Ln is any lanthanide, ormore particularly, La and/or Ce), Li₆Ln₂SrM₂O₁₂ (where M is Nb, Ta, orSb, and Ln is any lanthanide, or more particularly, La and/or Ce), andLi₆Ln₂BaM₂O₁₂ (where M is Nb, Ta, or Sb, and Ln is any lanthanide, ormore particularly, La and/or Ce).

In different embodiments, the recited oxygen value of “11.5” in formula(1) can be either a precise value, or alternatively, within a range ofthe indicated value: for example, ±0.5 of the indicated value (i.e.,11-12), ±0.4 (i.e., 11.1-11.9), ±0.3 (i.e., 11.2-11.8), ±0.2 (i.e.,11.3-11.7), ±0.1 (i.e., 11.4-11.6), or alternatively, only a positive ornegative value from the indicated value (e.g., +0.5 from the indicatedvalue, which corresponds to 11.5-12). Likewise, the recited oxygen valueof “12” can be either a precise value, or alternatively, within a rangefrom the indicated value: for example, ±0.5 of the indicated value(i.e., 11.5-12.5), ±0.4 (i.e., 11.6-12.4), ±0.3 (i.e., 11.7-12.3), ±0.2(i.e., 11.8-12.2), or ±0.1 (i.e., 11.9-12.1). Similarly, the value ofthe subscript on Li can be either the precise value, as indicated, oralternatively, a value of, for example, ±0.5, ±0.4, ±0.3, ±0.2, ±0.1,±0.05, ±0.5, ±0.2, −0.5, or −0.2 from the indicated value.

In a preferred embodiment, the oxide composition of the instantinvention, described above, is in the form of nanoparticles (i.e., isnanoparticulate). In some embodiments, the term “nanoparticles”, as usedherein, indicates individual (i.e., separate) particles having ananoscale size. In other embodiments, the term “nanoparticles”, as usedherein, refers to grains of the solid oxide material, as typically foundin crystalline, semicrystalline, or polycrystalline materials. Thenanoparticles generally have an average diameter of less than 1 micron.In different embodiments, the nanoparticles have an average diameter ofor less than 900 nm, 800 nm, 700 nm, 600 nm, 500 nm, 400 nm, 300 nm, 250nm, 200 nm, 150 nm, 100 nm, 90 nm, 80 nm, 70 nm, 60 nm, 50 nm, 40 nm, 30nm, 20 nm, 10 nm, 5 nm, or an average diameter within a range bounded byany of the foregoing exemplary values. In some embodiments, a portion ofthe oxide composition (e.g., at least 40, 50, 60, 70, 80, 90, 95, 98, or99%) is nanoparticulate in nature, while a portion is larger thannanoparticulate (e.g., greater than 1 micron, and up to, for example, 2,3, 4, 5, 10, 20, 50, or 100 microns in size). In other embodiments, theentire oxide composition is nanoparticulate in nature (e.g., within oneof the ranges set forth above). Moreover, in different embodiments, thenanoparticles are either completely monodisperse, or alternatively,possess some level of polydispersity (e.g., a standard deviation (SD)from the mean of or less than 100 nm, 50 nm, 20 nm, 10 nm, 5 nm, 4 nm,3, nm, 2 nm, or 1 nm).

In a particular embodiment, the nanoparticulate oxide compositiondescribed above is in the form of a powder. In some embodiments, theparticles of the powder are the same size as the nanoparticles of thesolid oxide material. In other embodiments, the particles of the powderare agglomerated forms of the nanoparticles of the solid oxide material.The agglomerated nanoparticles can, on average, have a size of any ofthe nanoparticle sizes set forth above, or alternatively, a larger sizeof, for example, 2, 3, 4, 5, 10, 20, 50, or 100 microns in size.

In another particular embodiment, the nanoparticulate oxide compositiondescribed above is in the form of a film. The film can have any suitablethickness, e.g., up to 1 millimeter (1 mm), 500 microns (500 μm), 100microns (100 μm), 50 microns (50 μm), 20 microns (20 μm), 10 microns (10μm), 5 microns (5 μm), or 1 micron (1 μm). In particular embodiments,the film is a thin film, i.e., up to or less than 1 micron in thickness.The thin film can have an average thickness of, for example, any of thenanoparticle sizes given above. As would be understood by one skilled inthe art, the film thickness is necessarily limited by the size of thesolid oxide particles. Furthermore, in preferred embodiments, thethickness of the film is substantially or completely uniform, as wouldbe determined by the uniformity in particle size.

In other embodiments, the nanoparticulate oxide composition describedabove is in the form of fibers or any of a variety of geometricalshapes. The fibers can be as thin as the thickness of the nanoparticles,and up to any suitable thickness (e.g., 1, 2, 5, 10, 50, or 100microns). Other geometrical shapes include plates and cubes.

The ion conductivity of the solid oxide material is generally greaterthan 1×10⁻⁸ S·cm⁻¹. In different embodiments, the solid oxide materialexhibits an ion conductivity of or greater than 1×10⁻⁸ S·cm⁻¹, 1×10⁻⁷S·cm⁻¹, 1×10⁻⁶ S·cm⁻¹, 1×10⁻⁵ S·cm⁻¹, 1×10⁻⁴ S·cm⁻¹, 5×10⁻⁴ S·cm⁻¹,1×10⁻³ S·cm⁻¹, or an ion conductivity within a range bounded by any ofthe foregoing exemplary values.

In another aspect, the invention is directed to methods for preparing alithium-conducting oxide material. In the method, a precursor solutionsusceptible to hydrolysis is first subjected to hydrolysis conditions.The precursor solution contains the elements (e.g., metals and oxidesource) necessary to make the solid oxide material. The hydrolysisconditions include, at minimum, contact of the precursor solution withwater. Generally, 1-2 vol % of water is more than sufficient to causecomplete hydrolysis. Particularly when small amounts of precursorsolution are used (e.g., a thin film), miniscule amounts of water, suchas the trace quantities found in typical or moistened air, can also besufficient for substantial or complete hydrolysis. A weak acid (e.g., acarboxylic acid) may also be included in trace amounts to facilitatehydrolysis. Generally, hydrolysis of the precursor solution results information of an initial solid or gel. Upon drying of the gel, the gel isgenerally transformed into a xerogel. In some embodiments, the xerogel,or a solid produced (i.e., precipitated) and separated at the outset,may be useful as a lithium-conducting electrolyte without furtherprocessing.

Generally, the dried gel or other solid initially produced by hydrolysisrequires a heat treatment to produce a final oxide material having theproper stoichiometric ratio of elements and physical characteristics.These properties can be analyzed by a variety of materialscharacterization techniques, most prominently x-ray diffraction (XRD)and related techniques to determine if the final product has beenachieved in a desired level of purity.

In one embodiment, the heat treatment of the initially hydrolyzedproduct includes one or more pyrolysis steps. During the pyrolysis step,chemical and physical rearrangements occur, often with emission ofresidual solvent and byproduct species (e.g., loss of Li₂O or LiOH). Insome embodiments, the pyrolysis step also causes the solid oxide tochange from an amorphous state to a crystalline, semi-crystalline, orpolycrystalline state. Typically, the pyrolysis step is conducted at atemperature of at least 200° C. and up to 700° C. for a time of up to 48hours, wherein, generally, higher temperatures require shorterprocessing times to achieve the same effect. In different embodiments,the temperature employed in the pyrolysis step is 200° C., 250° C., 300°C., 350° C., 400° C., 450° C., 500° C., 550° C., 600° C., 650° C., or700° C., or within a temperature range bounded by any two of theforegoing exemplary values. For any of these temperatures, or a rangetherein, the processing time (i.e., time the solid oxide is processed ata temperature or within a temperature range) can be, for example,precisely, at least, or no more than 15 minutes, 30 minutes, 1 hour, 2hours, 3 hours, 4 hours, 5 hours, 6 hours, 12 hours, 18 hours, 24 hours,30 hours, 36 hours, 42 hours, 48 hours, or within a time range boundedby any two of the foregoing exemplary values.

In further embodiments, the pyrolysis step described above can befollowed by a higher temperature sintering step to further encourageformation of a pure product. In some embodiments, the sintering step isemployed primarily to induce further crystallization, particularly whenthe product resulting from pyrolysis is found to retain an amorphousportion. Typically, the sintering step is conducted at a temperaturegreater than 700° C. and up to 1600° C. for a time of up to 48 hours,wherein, generally, higher temperatures require shorter processing timesto achieve the same effect. In different embodiments, the temperatureemployed in the sintering step is 750° C., 800° C., 850° C., 900° C.,950° C., 1000° C., 1050° C., 1100° C., 1150° C., 1200° C., 1250° C.,1300° C., 1350° C., 1400° C., 1450° C., 1500° C., 1550° C., or 1600° C.,or within a temperature range bounded by any two of the foregoingexemplary values. For any of these temperatures, or a range therein, theprocessing time can be, for example, any of the exemplary processingtimes or time ranges provided above for the pyrolysis step.

Generally, the one or more heat treatment steps are conducted undernormal atmospheric pressure. However, in some embodiments, an elevatedpressure (e.g., above 1 atm and up to 2, 5, 10 or 110 atm) is employed,while in other embodiments, a reduced pressure (e.g., below 1, 0.5, or0.2 atm) is employed. Furthermore, although the heat treatment steps aregenerally conducted under a normal air atmosphere, in some embodiments,an elevated oxygen, reduced oxygen, or inert atmosphere is used. Somegases that can be included in the processing atmosphere include, forexample, oxygen, nitrogen, helium, argon, carbon dioxide, and mixturesthereof.

Although in many embodiments the heat treatment step is conducted for anentire length of time at a particular temperature, it may be preferredto gradually increase and/or decrease the temperature during the heattreatment step between any of the temperatures given above, or betweenroom temperature (e.g., 15, 20, 25, 30, or 35° C.) and any of thetemperatures given above. In different embodiments, the gradual increaseor decrease in temperature can be practiced by employing a rate oftemperature change of, or at least, or no more than 1° C./min, 2°C./min, 3° C./min, 5° C./min, 7° C./min, 10° C./min, 12° C./min, 15°C./min, 20° C./min, 30° C./min, 40° C./min, or 50° C./min, or anysuitable range between any of these values. The gradual temperatureincrease can also include one or more periods of residency at aparticular temperature, and/or a change in the rate of temperatureincrease or decrease.

The precursor solution being hydrolyzed and optionally heat-treatedcontains all of the metals to be included in the solid oxide material.The metals in the precursor solution are included in molar ratios (i.e.,stoichiometric ratios) appropriate for producing a solid oxide materialof a desired formula. Generally, it has been found herein that a solidoxide material of a desired formula can be produced from a precursorsolution containing each of the metal species in molar ratiossubstantially corresponding (e.g., generally, within ±10%) to the molarratios of elements in the oxide material to be produced. However, inseveral embodiments of the instant method, it has been found beneficialto employ a molar amount of lithium that exceeds the stoichiometricamount (i.e. as indicated by the formula of the oxide material to beproduced) in order for a solid oxide material with the correctstoichiometric ratio of elements to be produced. In differentembodiments, the molar excess of lithium can be, for example, at least a50%, 100%, 150%, or 200% excess.

In a first set of embodiments, the precursor solution includes lithiumions and at least one type of pentavalent metal ion. The pentavalentmetal ion can be, for example, pentavalent niobium (Nb⁺⁵), tantalum(Ta⁺⁵), or antimony (Sb⁺⁵). In some embodiments, only one type ofpentavalent metal ion is included (such as any one of the foregoingtypes), while in other embodiments, two, three, or more differentpentavalent metal ions are included. The solution can also optionallyfurther include, for example, one or more alkali metal ions other thanlithium, and/or one or more alkaline earth metal ions, and/or one ormore transition metal ions other than Nb or Ta, and/or one or more maingroup metal ions other than Sb, and/or one or more rare earth (i.e.,lanthanide or actinide) metal ions.

In a second set of embodiments, the precursor solution includes lithiumions and at least one type of trivalent lanthanide metal ion. Thelanthanide metal can be any of the elements in the Periodic Table of theElements having an atomic number of 57 to 71, as described in furtherdetail above. In particular embodiments, at least one of the lanthanidemetals is La. The solution can also optionally further include, forexample, one or more alkali metal ions other than lithium, and/or one ormore alkaline earth metal ions, and/or one or more transition metalions, and/or one or more main group metal ions.

In a third set of embodiments, the precursor solution includes lithiumions, at least one pentavalent metal ion, and, in addition, at least onetype of trivalent lanthanide metal ion. The solution can also optionallyfurther include, for example, one or more alkali metal ions other thanlithium, and/or one or more alkaline earth metal ions, and/or one ormore transition metal ions other than Nb or Ta, and/or one or more maingroup metal ions other than Sb.

The metals included in the precursor solution are associated or bound tonegatively charged ligands. The ligand can be monodentate or polydentate(e.g., bidentate, tridentate, or tetradentate). In order for theprecursor solution to undergo hydrolysis, at least a portion of theligands are alkoxide ligands. In some embodiments, the ligands areentirely alkoxide ligands. The alkoxide ligands primarily consideredherein are those having the formula —OR, where R is a hydrocarbon group,generally of 1 to 6 carbon atoms, and the hydrocarbon group can be, forexample, saturated or unsaturated, straight-chained or branched, andcyclic or acyclic. Some typical examples of R include methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl,2-methoxyethyl (CH₃OCH₂CH₂), trifluoromethyl, vinyl, allyl, cyclopentyl,cyclohexyl, phenyl, tolyl, and benzyl. The alkoxide ligand can also havemore than one alkoxy portion, e.g., a di- or tri-alkoxide.

In particular embodiments, in addition to alkoxide ligands, at least aportion of the ligands are β-diketone ligands. A common β-diketoneligand useful herein is acetylacetone (i.e., 2,4-pentanedione, or“acac”). Other examples of β-diketone ligands include 2,4-hexanedioneand 3,5-heptanedione.

In particular embodiments, in addition to alkoxide ligands, at least aportion of the ligands are carboxylate ligands. Some examples ofcarboxylate ligands include those having up to six, seven, or eightcarbon atoms, e.g., acetate, propionate, butyrate, valerate, benzoate,malonate, fumarate, and succinate. In further embodiments, alkoxideligands are used in combination with at least one β-diketone ligand andat least one carboxylate ligand.

In some embodiments, the precursor solution is hydrolyzed and heattreated in bulk form, i.e., in a container (e.g., tube, flask, orcrucible). Generally, such a methodology will produce a solid mass thatcan be turned into a powder by further processing, such as bytrituration, or by partial dissolution or loosening with a non-aqueoussolvent, optionally aided by, for example, sonication, grinding, ballmilling, and/or stirring.

In other embodiments, the precursor solution is deposited as a film ontoa substrate before hydrolysis and heat treatment. The film of precursorsolution can be of any desired thickness, as described above. Inparticular embodiments, the film of precursor solution is a thin film,as described above. The film of precursor solution can be applied by anysuitable method known in the art, including, for example, by dipcoating, brush coating, spin coating, and spraying. The substrate can beany substrate that can benefit by deposition thereon of alithium-conducting solid oxide material. Particularly considered hereinare those substrates that can be utilized as a component in alithium-ion battery, particularly an electrode (i.e., cathode and/oranode) of a lithium-ion battery. Some examples of substrates includelithium, lithium alloys, carbon, graphite-lithium intercalationmaterials, lithium-containing oxide materials (e.g., LiCoO₂ andLi₂Mn₂O₄), lithium-conducting polymer electrolyte materials (e.g.,polyacrylonitrile, polyvinylidene fluoride, or polyethylene oxide),silica, silicates, and metals, such as aluminum, tin, or any of thetransition metals enumerated above, as well as alloys or oxides of thesemetals.

The metals, ligands, and any other solutes of the precursor solution areheld (i.e., dissolved) in a non-aqueous solvent. The solvent can be, forexample, an organic polar protic or non-protic solvent. Some examples oforganic polar protic solvents include alcohols, e.g., methanol, ethanol,n-propanol, isopropanol, n-butanol, isobutanol, ethylene glycol, and thelike. Some examples of organic polar non-protic solvents includeacetonitrile, dimethylformamide, dimethylsulfoxide, methylene chloride,organoethers (e.g., tetrahydrofuran, dimethoxyethane, and diethylether),and the like. In some embodiments, a lower boiling point solvent ispreferred (e.g., a boiling point up to or less than 25, 30, 35, 40, 45,50, 55, or 60° C.), while in other embodiments a higher boiling pointsolvent is preferred (e.g., a boiling point of at least or greater than65, 70, 75, 80, 85, 90, 95, 100, or 110° C.). In other embodiments, thesolvent has a boiling point within a range bounded by any two of theforegoing exemplary boiling point temperatures.

A class of lithium ion precursor compounds useful as a source of lithiumin the precursor solution include those of the formula LiX, wherein X ispreferably an anion selected from alkoxide (OR, as defined above),β-diketonate, or carboxylate. The lithium precursor compound can also beheterometallic, such as LiM(OR)₆, LiM(OR)₆-n(acac)_(n), and LiLn(OR)₄,wherein M is a pentavalent metal ion (e.g., pentavalent Nb, Ta, or Sb),Ln is a lanthanide metal (for example, La or Ce), and n is a value of 0,1, 2, 3, 4, 5, or 6, or within a range therein. Some classes ofpentavalent metal ion precursor compounds useful as a source ofpentavalent metal in the precursor solution include those of the formulaM(OR)₅, and LiM(OR)_(6−n)(acac)_(n), described above. Some classes oflanthanide metal ion precursor compounds useful as a source oflanthanide metal in the precursor solution include those of the formulaLn(OR)₃, Ln(OR)_(3−n)(acac)_(n), and LiLn(OR)₄, wherein Ln is alanthanide metal and n is a value of 0, 1, 2, or 3, or within a rangetherein. If an alkaline earth metal is desired to be included, analkaline earth precursor compound of, for example, formula A(OR)₂,A(OR)(acac), or A(acac)₂ can be included, wherein A is an alkaline earthmetal, as described in further detail above.

In some embodiments, it is particularly advantageous to incorporate intothe precursor solution a heterometallic alkoxide composition (i.e.,compound or material) that includes at least one pentavalent metal, atleast one trivalent lanthanide metal, and negatively charged ligands, atleast one of which is an alkoxide ligand. The ligands are associated,and more typically, bound, to the metal ions, thereby forming ametal-ligand complex. Since heterometallic alkoxides generally hydrolyzewithout dissociation, the M-OR-M′ bond is replaced by M-OH-M′ bonds inheterometallic alkoxides during hydrolysis. The M-OH-M′ bonds areconverted to M-O-M′ bonds after hydrolysis. In comparison, a mixture ofalkoxides form a mixture of hydroxides (e.g., M-OH-M, M-OH-M′, andM′-OH-M′) which form corresponding metal-oxide-metal bonds by adiffusion-controlled process during pyrolysis and sintering.Accordingly, at least one advantage in using a heterometallic alkoxidecomposition is that a metal oxide composition with desiredmetal-oxide-metal bonds can be produced with minimal amounts of unwantedmetal-oxide-metal bonds.

In a particular embodiment, the heterometallic alkoxide composition hasthe following formula:LnM₂X₁₃  (3)

In formula (3) above, Ln represents at least one trivalent lanthanidemetal, M represents at least one pentavalent metal, and X isindependently selected from negatively charged ligands, at least one ofwhich represents an alkoxide ligand. In particular embodiments, Mrepresents pentavalent niobium, tantalum, or antimony, or a combinationthereof. In other or further embodiments, Ln represents La or Ce, or anyof these lanthanide metals in combination with another lanthanide metalor doped with another metal.

Some more specific examples of compositions according to formula (3)include LaNb₂(OR)₁₃, LaTa₂(OR)₁₃, LaSb₂(OR)₁₃, CeNb₂(OR)₁₃, CeTa₂(OR)₁₃,CeSb₂(OR)₁₃, NdNb₂(OR)₁₃, NdTa₂(OR)₁₃, NdSb₂(OR)₁₃, SmNb₂(OR)₁₃,SmTa₂(OR)₁₃, SmSb₂(OR)₁₃, EuNb₂(OR)₁₃, EuTa₂(OR)₁₃, EuSb₂(OR)₁₃,GdNb₂(OR)₁₃, GdTa₂(OR)₁₃, GdSb₂(OR)₁₃, DyNb₂(OR)₁₃, DyTa₂(OR)₁₃,DySb₂(OR)₁₃, YbNb₂(OR)₁₃, YbTa₂(OR)₁₃, and YbSb₂(OR)₁₃, wherein R hasbeen defined above. In further embodiments, one or more of the ORligands can be substituted by one or more β-diketonate or carboxylateligands.

In other embodiments, it is particularly advantageous to incorporateinto the precursor solution a heterometallic alkoxide composition thatincludes at least one pentavalent metal, at least one alkaline earthmetal, and negatively charged ligands, at least one of which is analkoxide ligand. In a particular embodiment, the heterometallic alkoxidecomposition has the following formula:AX′₂MX₅  (4)

In formula (4) above, A represents at least one alkaline earth metal, Mrepresents at least one pentavalent metal, and X and X′ areindependently selected from negatively charged ligands, provided that atleast one of X represents an alkoxide ligand. In particular embodiments,M represents pentavalent niobium, tantalum, or antimony, or acombination thereof. In other embodiments, A represents Ca, Sr, or Ba,or a combination thereof.

Some more specific examples of compositions according to formula (4)include Mg(OR)₂Nb(OR)₅, Ca(OR)₂Nb(OR)₅, Sr(OR)₂Nb(OR)₅, Ba(OR)₂Nb(OR)₅,Mg(OR)₂Ta(OR)₅, Ca(OR)₂Ta(OR)₅, Sr(OR)₂Ta(OR)₅, Ba(OR)₂Ta(OR)₅,Mg(OR)₂Sb(OR)₅, Ca(OR)₂Sb(OR)₅, Sr(OR)₂Sb(OR)₅, Ba(OR)₂Sb(OR)₅,Mg(acac)₂Nb(OR)₅, Ca(acac)₂Nb(OR)₅, Sr(acac)₂Nb(OR)₅, Ba(acac)₂Nb(OR)₅,Mg(acac)₂Ta(OR)₅, Ca(acac)₂Ta(OR)₅, Sr(acac)₂Ta(OR)₅, Ba(acac)₂Ta(OR)₅,Mg(acac)₂Sb(OR)₅, Ca(acac)₂Sb(OR)₅, Sr(acac)₂Sb(OR)₅, andBa(acac)₂Sb(OR)₅.

In one embodiment, the precursor solution is provided as a singlesolution containing all components necessary for synthesizing a desiredsolid oxide material. In other embodiments, two or more solutions areprovided to prepare the precursor solution containing all componentsnecessary for synthesizing a desired solid oxide material. To preparethe precursor solution, the two or more solutions, or portions thereof,are combined. Each of the solutions to be combined contains some, andnot all, of the components necessary for synthesizing a desired solidoxide material. In some embodiments, the two or more solutions to becombined are conveniently provided as a package, such as in the form ofa kit. The kit can optionally include instructions specifying theamounts and manner of use of the solutions, as encompassed by theabove-described methodology. In yet other embodiments, the precursorsolution is prepared from a concentrate, i.e., by appropriate dilutionof the concentrate.

In another aspect, the invention is directed to a lithium ion batterythat contains any of the lithium-containing solid oxide compositionsdescribed above. The lithium ion battery can have any of thearchitectures and designs of lithium ion batteries known in the art.Some types of lithium ion batteries particularly considered include theconventional lithium ion battery (i.e., that use as an electrolyte alithium salt in an organic solvent), lithium ion polymer battery, andlithium air battery. As known in the art, some common features oflithium ion batteries include a negative electrode (often referred to asthe anode), positive electrode (often referred to as a cathode), and alithium-conducting electrolyte (typically, an organic solvent, such asan ether or organic carbonate) that transports lithium ions between thetwo electrodes during charging and discharging.

Numerous materials may be used as the positive or negative electrode.The choice of electrode material depends to a large extent on theconstruction of the lithium ion battery (e.g., compatibility of theelectrode material with other components of the battery), desiredperformance characteristics (e.g., energy and power densities), andapplication. Some examples of anode materials include graphite (i.e.,intercalated lithium graphite), lithium metal, lithium alloy (e.g.,lithium-aluminum or lithium-indium), lithium-containing polyatomic aniontransition metal compounds (e.g., LiTi₂(PO₄)₃), and lithium-containingtransition metal oxides, particularly of titanium or vanadium, such asLi₄Ti₅O₁₂. Some examples of cathode materials include layered oxidematerials (e.g., lithium-containing transition metal oxides, such asLiCoO₂, LiNiO₂, LiMnO₂, and LiNi_(x)Mn_(y)Co_(z)O₂, wherein x, y, and zsum to 1, and at least one, two, or all of x, y, and z are non-zero),lithium-containing polyatomic anion transition metal compounds (e.g.,LiFePO₄ and Li₂FePO₄F), and lithium-containing spinel oxides (e.g.,Li₂Mn₂O₄). Typically, the electrode materials are configured as a layeron a base metal, such as aluminum, carbon, or stainless steel. Ifdesired or found necessary, the electrode materials can also include anelectron conduction additive, ion conduction additive, or both. Someexamples of electron conduction additives include conductive carbon,metal powder, and conductive polymers. Some examples of ion conductionadditives include lithium ion conductive crystals or glass-ceramics. Inparticular embodiments, an electron conduction and/or ion conductionadditive is excluded. In other embodiments, one or both of the electrodematerials are doped with a conductivity enhancement material, such asniobium, aluminum, or zirconium. The solid oxide electrolyte may also bedoped.

In particular embodiments of the invention, a film of the solid oxidematerial described above is situated between the two electrodes and incontact with the two electrodes. Such a composite structure can beassembled by any of the methods known in the art. For example, a sheetof the solid oxide material can be placed between the two electrodematerials, followed by heat pressing (e.g., by heating and rollpressing). The resulting laminate material can be appropriately cut tosize and sealed. Lead lines and other device components can be installedduring the sealing process, or sometime thereafter. Alternatively, afilm (i.e., coating) of a precursor solution of the solid oxide materialcan be placed on either or both (e.g., between) the electrode materials,and this followed by hydrolysis and heat treatment operations forconversion of the precursor to the solid oxide material. In furtherembodiments, one, two, or more layers of another material can besituated between the electrode material and the solid oxide. Theadditional layer can serve any suitable function, such as to preventcontact of the electrode material with the oxide material if thesematerials are incompatible, or to adjust, improve, or optimize acharacteristic, such as electron or ion conduction.

Generally, the solid oxide material described herein is employed as anelectrolyte in place of (i.e., in the absence of) a liquid or polymerelectrolyte. However, some embodiments may employ the solid oxidematerial described herein in tandem with either a liquid or polymerelectrolyte material. The liquid or polymer electrolyte material mayfurther include one or more lithium salts. Some examples of lithiumsalts include LiBF₄, LiPF₆, LiAsF₆, Li₂SO₄, and LiCF₃SO₃ (lithiumtriflate). If permitted by the composition of the electrodes and othercomponents of the battery, a liquid or polymer electrolyte can includean amount of water.

Examples have been set forth below for the purpose of illustration andto describe certain specific embodiments of the invention. However, thescope of this invention is not to be in any way limited by the examplesset forth herein.

Example 1 Solution Synthesis of La₃Li₅Nb₂O₁₂ and Analysis Thereof

A mixture of Nb(OC₂H₅)₅ (0.76 g), La(O-i-C₃H₇)₃ (1.14 g), and LiO-i-C₃H₇(0.39 g) in 2-propanol (40 mL) was stirred to obtain a homogenous clearsolution. Without being bound by any theory, it is believed that thissolution is a mixture of LiNb(OC₂H₅)₆, 3La(O-i-C₃H₇)₃ and LiO-i-C₃H₇ inapproximately a 2:3:3 ratio. In some cases, the clear solution wascooled (e.g., down to −78° C.), while in other cases, the clear solutionwas kept at room temperature. The stirring was continued until formedsolids made stirring difficult or impossible. Upon careful hydrolysiswith 0.72 g of water, a white gel was obtained, which, upon drying undervacuum or slow evaporation, furnished a xerogel. X-ray powderdiffraction (XRD) analysis showed the xerogel to be amorphous. Thepyrolysis of this powder at 600° C. for 4 hours resulted in acrystalline powder, which was identified to be primarily LiLa₂NbO₆materials. These results suggest that there are amorphous La₂O₃ and Li₂O(or LiOH) components in the powder. Sintering of the powder at 800° C.for 4 hours resulted in the crystallization of La₃Li₅Nb₂O₁₂ whileresidual LiLa₂NbO₆ was still present. Further sintering at 800° C. for24 hours did not result in any change in the XRD pattern.

The foregoing results suggest loss of Li₂O (or LiOH) during processing.Accordingly, in an effort to achieve a pure sample of La₃Li₅Nb₂O₁₂, theabove preparation was repeated, this time using a 100% excess of lithium(i.e., a total of 0.78 g LiO-i-C₃H₇). The resulting xerogel, uponthermal treatment at 800° C. for 4 hours furnished a pure sample ofLa₃Li₅Nb₂O₁₂. The foregoing results demonstrate that a pure sample ofLa₃Li₅Nb₂O₁₂ was achieved by employing an excess of lithium.

Example 2 Alternate Solution Synthesis of La₃Li₅Nb₂O₁₂ and AnalysisThereof

The reactants Nb(OC₂H₅)₅ (0.76 g), La(O-i-C₃H₇)₃ (1.14 g), andLiO-i-C₃H₇ (0.78 g) in 2:3:10 molar ratio were mixed in tetrahydrofuran(THF) and hydrolyzed with water. The resulting gel was dried andpyrolyzed, as described in Example 1, to obtain pure La₃Li₅Nb₂O₁₂. Theexcess Li(OR) in the reaction mixture was found to be necessary tocounterbalance the loss of Li₂O during pyrolysis. The sole FIGURE showsthe XRD pattern of the product. Employing the Scherrer equation, theparticle size has been calculated from the XRD pattern to be 28 nm.

While there have been shown and described what are at present consideredthe preferred embodiments of the invention, those skilled in the art maymake various changes and modifications which remain within the scope ofthe invention defined by the appended claims.

What is claimed is:
 1. A composition comprised of nanoparticles oflithium ion conducting solid oxide material, wherein the lithium ionconducting solid oxide material is an oxide composition comprised oflithium ions, and at least one type of metal ion selected frompentavalent metal ions and trivalent lanthanide metal ions, wherein saidnanoparticles have an average diameter of up to 5 nm.
 2. The compositionof claim 1, wherein the lithium ion conducting solid oxide material isan oxide composition comprised of lithium ions, at least one type ofpentavalent metal ion, and at least one type of metal ion selected fromtrivalent lanthanide metal ions and alkaline earth metal ions.
 3. Thecomposition of claim 2, wherein the lithium ion conducting solid oxidematerial comprises at least one material selected from among materialshaving the following formulas:Li_(5+x)Ln₂AM₂O_(11.5+0.5x)  (1)andLi_(5+y)A_(y)Ln_(3−y)M₂O₁₂  (2) wherein A represents at least onealkaline earth metal, M represents at least one pentavalent metal, Lnrepresents at least one trivalent lanthanide metal, and x and y are,independently, a number from 0 to
 2. 4. The composition of claim 1,wherein said pentavalent metal ions are selected from pentavalentniobium, tantalum, and antimony ions.
 5. The composition of claim 1,wherein said composition is in the form of a powder.
 6. The compositionof claim 1, wherein said composition is in the form of a thin film up to1 micron in thickness.
 7. The composition of claim 1, wherein saidnanoparticles have an average diameter of less than 5 nm.